Lead and leadset designs for providing medical telemetry antenna

ABSTRACT

Various designs and features of an ambulatory transceiver and ECG lead set are disclosed for use in remote patient monitoring. One feature involves the use of unshielded, dual-conductor lead wires in which one conductor carries the patient&#39;s ECG signal and the other conductor provides an RF antenna element for the transceiver. The lead wires used in one embodiment provide improved flexibility, durability, and antenna performance over conventional lead sets with shielded wires. Another feature involves an antenna diversity scheme in which the transceiver switches between two or more ECG-lead antennas, each of which is formed from one or more ECG leads of the lead set. Another feature involves the use of a circuit within the transceiver to monitor, and dynamically compensate for changes in, the impedance of an ECG-lead antenna or a conductor thereof. Another feature is an improved circuit for protecting the transceiver from damage caused by defibrillation pulses.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Appl. No.60/273,136, filed Mar. 2, 2001, titled REMOTE TRANSCEIVER AND LEAD SETDESIGNS FOR MEDICAL TELEMETRY.

FIELD OF THE INVENTION

The present invention relates to telemetry systems for remote patientmonitoring. More specifically, the invention relates to the use ofleads, such as ECG (electrocardiograph) leads, to provide antennas forambulatory or other remote telemetry devices.

BACKGROUND OF THE INVENTION

A variety of patient monitoring systems exist that allow the physiologicdata of patients within a medical facility to be monitored remotelyusing wireless communications. These systems commonly include remotetransmitters or transceivers that collect, and transmit over a wirelesschannel, the physiologic data of respective patients. This physiologicdata may include, for example, real-time electrocardiograph (ECG)waveforms, SpO₂ levels, and non-invasive blood pressure readings. Thetransmitted physiologic data is conveyed to one or more centralizedmonitoring stations within the medical facility. From such a monitoringstation, a clinician can visually monitor the physiologic status, inreal time, of many different patients. The monitoring stations may alsorun automated monitoring software for detecting and alerting personnelof certain types of physiologic events, such as the occurrence of acardiac arrhythmia condition.

To enable patients to be monitored while ambulatory, some systemsinclude battery-powered remote transceiver devices that are adapted tobe worn by or attached to patients while ambulatory (“ambulatorytransceivers”). Each ambulatory transceiver attaches to a patient by apouch or other attachment device, and senses the patient's physiologicdata via a set of ECG leads (and/or other types of sensor leads). In onecommon design, each lead wire of the ECG lead set is constructed of ashielded wire (typically coaxial) comprising an inner conductorsurrounded by a mesh shield. The inner conductor electrically connectsan ECG sensor to the ambulatory transceiver's sensor circuitry, and isused to carry ECG signals. The outer shield protects the ECG signalsfrom radio frequency (RF) interference. In other designs, each lead wireis an unshielded, single-conductor wire.

In some prior art designs, selected portions of the ECG lead wires areused as the RF telemetry antenna. For example, in one design in whichthe lead wires have outer shields that are a fractional length of thetotal wire length, the shields of multiple lead wires are connectedtogether to form the antenna. In another design, the multi-strandconductor of the RL (right leg) lead wire is used as the antenna. Animportant benefit of these designs is that they eliminate the need for adedicated antenna mounted to or inside the transceiver's housing. Inaddition, a lead antenna can provide a somewhat larger aperture, andthus better RF link performance, than a housing mounted antenna.

SUMMARY

One problem with existing designs is that the coaxial ECG lead wirestend to be relatively stiff in comparison to other types of wires. As aresult, the leads cause discomfort to patients and tend to lackdurability.

Another problem with existing designs, and particularly with ambulatorytransmitter and transceiver designs, is that data transmissions arehighly susceptible to attenuation caused by the patient's body or nearbyobjects. This problem is frequently experienced when the patient is inbed. For example, if the patient rolls over on top the antenna(dedicated or ECG lead), the patient's body may block signaltransmissions to and from the ambulatory device. Further, the patient'sposition in bed may cause a portion of the antenna to be positionedclose to a bed rail or other grounded metal object, causing the entireantenna to de-tune. In these situations, the patient's real timephysiologic data typically can not be remotely monitored with sufficientreliability.

Yet another problem with existing telemetry devices, and other types ofdevices that receive signals from an ECG lead set, is that they do notprovide an adequate solution to the problem of protecting againstdefibrillation pulses. For example, some designs merely usecurrent-limiting resistors connected along the ECG signal lines. Theseresistors tend to be large, high-power components, and tend to increasethe manufacturing cost of the device while providing only limitedprotection.

The present invention addresses these and other problems with prior artdesigns by providing several inventive features that may be usedindividually or in appropriate combination. One such feature involvesthe replacement of some or all of the conventional lead wires with leadwires having two side-by-side conductors. In each such lead, one of thetwo conductors is used to carry ECG signals, and the other is used as anantenna element. An important benefit of this design feature is that theleads are generally more flexible, and lighter in weight, than coaxialleads. As a result, the leads provide greater comfort to patients.Further, in comparison to typical lead wire antenna designs in which thecoaxial shield extends only a few inches, the use of an antennaconductor that extends substantially the entire length of the lead wire(as in the preferred embodiment) provides improved antenna performance.Additional benefits include greater lead durability and lower cost oflead material. This and the other features of the invention may also beused with other types of lead sets for sensing physiologic data, such asEEG lead sets and leads sets with SpO2 and oscillometric blood pressuresensors.

Another feature involves statically or dynamically dividing the set ofECG or other leads into two or more groups to provide two or morecorresponding telemetry antennas. For example, in a lead set with fiveECG leadwiress, the antenna portions of the RL (Right Leg) and C (Chest)leads may be electrically connected to form a first antenna, and theantenna portions of the LA (Left Arm), LL (Left Leg) and RA (Right Arm)leads may be interconnected to form a second antenna. The leads may, forexample, be constructed with conventional coaxial lead wires in whichthe outer shields are used as the antenna portions, or may beconstructed with wires having side-by-side conductors as describedabove. To provide diversity, a control circuit within the transceiverselects between the multiple antennas, preferably based on observedcharacteristics of received RF transmissions. Thus, for example, whenone antenna produces data errors as the result of a lead touching a bedrail, the control circuit may switch to an antenna that does not use theaffected lead. In embodiments in which the telemetry device transmitsbut does not receive data via the antenna used to transmit, the antennadiversity may be selected using antenna impedance measurements (asdescribed below). Alternatively, the telemetry device may simplytransmit the same data separately using each antenna to provideredundant transmissions.

In one embodiment, the ECG leads are statically grouped to form themultiple antennas—preferably by fixed electrical connection of antennaconductors within the lead set's connector plug. In another embodiment,the antenna portions of the ECG leads are connected to an electricalswitch, such as a matrix switch capable of selecting any combination ofone or more ECG leads to use as the antenna. The switch is controlled bya control circuit that dynamically selects the one or more leads to useto form the antenna based on observed signal characteristics andpredefined selection criteria.

Another feature, which may be used alone or in combination with theabove-mentioned features, involves the use of an impedance detector tomonitor the impedance of an ECG-lead antenna (or an antenna thatincludes conductors within other types of leads). The output of theimpedance detector may be used to control an impedance matching circuitto maintain the ECG lead antenna in a tuned state. For example, when theantenna's impedance changes as the result of proximity to a bed rail,the antenna's impedance matching circuit may be dynamically adjusted tomaintain the antenna in an optimal state.

The antenna impedance measurements may additionally or alternatively beincorporated into the decision logic used to select an antenna. Forexample, in one embodiment, an impedance detector is integrated with theabove-mentioned matrix switch, and is used to separately monitor theimpedance of the antenna portion of each ECG or other lead. Theseimpedance measurements are used (preferably in combination with receivedsignal-quality measurements) to select the lead or leads to use to formthe antenna. For example, when the impedance associated with aparticular lead falls outside of a predefined range, that lead mayautomatically be excluded from potential use as or within an antenna.

Another feature of the invention involves using the multiple antennaconductors of the coaxial or non-coaxial leads as elements of a phasedantenna array. In one embodiment of a transceiver system, each suchantenna conductor is coupled to a respective phase shifter capable ofadjusting the phases of signals received and radiated by that antennaconductor. During receive events, a phase detection circuit monitors thephases of the respective RF signals received by the antenna conductors,and controls the phase shifters to compensate for phase differences.During transmission events, the phase shifters are used to effectivelysteer the beam formed by the antenna array in the direction of areceiving station and/or to reject an interference source. The antennabeam may also be steered passively (without transmitting) to locate abase station.

Another inventive feature, which similarly may be used alone or incombination with the aforementioned features, is an improved circuit forprotecting the remote transceiver's circuitry, or the circuitry ofanother type of device that receives signals from an ECG lead set, fromdamage caused by defibrillation pulses. In a preferred embodiment, thecircuit includes a low capacitance, transient voltage suppression (TVS)circuit connected between the ECG signal path and ground, and furtherincludes a current-limiting resistor connected in-line along the signalpath. Separate protection circuits of this type may be provided alongeach ECG signal path. The use of low capacitance TVS circuits allowssmall, low cost, surface-mount current limiting resistors to be used inplace of the relatively large current-limiting resistors used inconventional designs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other inventive features will now be described with referencesto the following drawings.

FIG. 1A illustrates an ambulatory transceiver device and representativeECG lead set according to a preferred embodiment of the invention.

FIG. 1B is a broken-away view taken along line 1A—1A of FIG. 1B, showingthe inner construction of a representative lead wire.

FIG. 2 illustrates an antenna diversity feature of the ambulatorytransceiver device and ECG lead set of FIG. 1.

FIG. 3 illustrates the general positions and configurations of theantennas of FIG. 2 when the ambulatory transceiver device andrepresentative lead set are attached to a patient.

FIG. 4A illustrates the configuration of the connector plug of the ECGlead set.

FIG. 4B is a cross sectional view taken along the line 4B—4B of FIG. 4A,showing the arrangement of five dual-conductor lead wires extendingoutward from the connector overmolding.

FIGS. 5A-5G illustrate the electrical connections within the connectorplug of FIG. 4 for each of seven different ECG lead sets that may beused with the ambulatory transceiver device.

FIG. 6 illustrates the circuitry of the ambulatory transceiver device infurther detail.

FIG. 7 illustrates a dynamic impedance matching feature that may beadded to the ambulatory transceiver design.

FIG. 8 illustrates the use of a matrix switch to select the ECG lead orleads to use as an antenna.

FIG. 9 illustrates an embodiment in which the multiple antennaconductors of the ECG leads are used as elements of a phased antennaarray.

Throughout the drawings, reference numbers are reused to indicatecorrespondence between referenced components.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An ambulatory transceiver system that embodies some of the inventivefeatures mentioned above will now be described with reference to FIGS.1-6. Additional designs incorporating other inventive features will thenbe described with reference to FIGS. 7-9. As will be apparent, many ofthe disclosed features can be used or practiced independently of others,and without many of the implementation-specific details set forthherein. In addition, many of the inventive features that are describedseparately can be appropriately combined within an ambulatory or othertelemetry device.

Although the specific embodiments illustrated in the drawings involve atransceiver unit that attaches to an ECG lead set, many of the disclosedfeatures may be embodied within or used with other types of devices.Examples of other devices include patient telemetry devices that aremerely RF transmitters and not RF receivers (referred to herein as“unidirectional transmitters”), and devices that sense physiologic dataother than ECG data. Specific examples of embodiments that involvealternative device types are set forth in the text below.

Throughout the following description, the term “coaxial” refersgenerally to the positional relationship between conductors (i.e., aninner conductor extends within an outer, tubular conductor). The term“coaxial wire” or “coaxial cable” additionally implies that the innerconductor and outer conductor are separated by a dielectric core. Theterm “shielded wire” refers to a wire in which the inner and outerconductors are arranged coaxially and may, but need not, be separated bya dielectric core (i.e., a shielded wire may, but is not necessarily, acoaxial wire).

FIGS. 1-6 illustrate the design of an ambulatory transceiver 30 and ECGlead set 32 according to a preferred embodiment of the invention. Theambulatory transceiver 30 is a portable, battery-powered telemetrydevice adapted to be worn by an ambulatory or non-ambulatory patient.The device 30 operates generally by receiving the patient's ECG signalsvia the lead set 32, and transmitting the ECG signals in real time viaRF as packetized data. The device 30 may also monitor and transmit othertypes of physiologic data of the patient via additional leads or sensors(not shown), such as respiration signals, SpO² levels, and NIBP(non-invasive blood pressure).

In one implementation, the ambulatory transceiver 30 is designed tocommunicate bi-directionally with access point transceivers (“accesspoints”) positioned throughout patient areas of a medical facility, asdescribed generally in U.S. Pat. No. 5,944,659, and co-pending U.S.application Ser. No. 09/615,362, filed Jul. 13, 2000, the disclosures ofwhich are hereby incorporated by reference. In other embodiments, theambulatory transceiver 30 may communicate with a different type of basestation, such as a PC with an RF modem. Thus, as used herein, the term“base station” is intended to refer generally to any type of device thatreceives telemetry data from a remote transceiver by wirelesscommunications.

As illustrated in FIG. 1A, the ambulatory transceiver 30 includes a leadset connector 35 that receives a connector plug 34 of the ECG lead set32. The physical configuration of the connector plug 34 is illustratedin FIGS. 4A and 4B (discussed below). In other embodiments, the lead setmay be fixedly attached to the transceiver 30 or other transmittingdevice.

The ambulatory transceiver 30 also includes an input/output (I/O)connector 36 that receives the plug 37 of an I/O cable. The I/Oconnector 36 allows the ambulatory transceiver 30 to be connected, ifdesired, to an external device having a standard RS-232 port (or a portwhich uses another interface standard), such as a mobile blood pressuresensor, an infusion pump, a ventilator, or a PDA (personal digitalassistant). Physiologic or other data received from the external deviceis transmitted by the ambulatory transceiver 30 together with thepatient's ECG waveforms, allowing such data to be remotely monitored inreal time. The I/O connector 36 may also be used to upload code updatesand perform other maintenance related tasks.

I. Lead Set Construction

In the embodiment shown in FIGS. 1-4, the lead set 32 has five leads 38for sensing ECG signals from the standard left arm, right leg, chest,right arm and left leg positions. Lead sets with three, four, and sixleads are also provided for use with the same ambulatory transceiver 30,as described below and illustrated in FIGS. 5C—5G. Each lead 38 of theillustrated lead set 32 is terminated with a snap connector 40 (FIG. 1A)for attachment to an ECG electrode on the patient's skin. Other types ofelectrode connectors, such as pinch clip connectors, may also be used.Leads or sensors for sensing other types of physiologic data mayoptionally be included within the same lead set 32.

In accordance with one feature of the invention, each ECG lead 38 isconstructed with an insulated wire 42 having two, multi-strandconductors 44, 46 (FIG. 1B) positioned generally parallel to one anotherin a non-coaxial arrangement from the connector plug 34 to the electrodeconnector 40. One of the two conductors 46 in each lead 38 is used tocarry the patient's ECG signal. This ECG conductor 46 is electricallyconnected to the conductive contact portion (not shown) of the electrodeconnector 40. The other conductor 44 is used as an antenna element forproviding a telemetry antenna (referred to herein as an “ECG-leadantenna”). As described below, the antenna conductors 44 of multipleleads 38 may optionally be connected to form a multiple-lead antenna. Inaddition, two or more separate ECG lead antennas may be formed toprovide antenna diversity.

In the illustrated embodiment in which the telemetry unit is atransceiver 30, the ECG-lead antenna or antennas are used forbi-directional RF communications with one or more base stations. TheECG-lead antennas may also be used to communicate with other types ofdevices, such as beacons or chirpers used to monitor patient location.Each antenna conductor 44 has a free end (not shown) terminated withinthe insulating material or free air space of the corresponding electrodeconnector 40. Although the terms “ECG conductor” and “antenna conductor”are used herein, it should be understood that these conductors may alsobe used for other purposes. In embodiments in which the telemetry unitis a unidirectional transmitter, the ECG-lead antennas are used only fortransmitting data.

The use of a lead wire 42 in which the conductors 44 are arrangedside-by-side, rather than coaxially as in conventional systems,advantageously allows wires with greater flexibility to be used. As aresult, a greater degree of patient comfort and lead durability can beachieved. This implementation has also been found to produce improvedantenna performance over designs in which the antenna is formed from theouter shields that extend along a small portion of each lead wire. Thisfeature of the design may, but need not, be implemented in combinationwith an antenna diversity scheme as described below. The characteristicsof the lead wires 42 used in one embodiment are listed in Table 1.

TABLE 1 Example Lead Wire Construction Wire Type bonded 2-conductorcable Conductor (44, 46) Tinsel with seven cores of Kevlar, each with asingle serve metal wrap of silver plated tinsel (T-3922) InsulatorMedical grade polyurethane, temp. rating +105° C. to −25° C. Outerdiameter (D in FIG. 1A) 0.080 inches Max resistance 0.210 ohms/foot Min.break load 40 lbs.

Lead wires constructed as set forth above may also be incorporated intoleads and lead sets for monitoring other types of physiologic data. Forinstance, the same or a similar lead wire construction may be usedwithin an electroencephalogram (EEG) lead set (in which case the ECGelectrodes would be replaced with EEG electrodes), or within a leadhaving an oscillometric blood pressure sensor. As with the ECG lead setdescribed above, one of the side-by-side conductors carries thepatient's physiologic data signal to the RF transmitter or transceiver,and the other is used as an antenna element for telemetry. The antennadiversity scheme described in the following section may also be usedwith such alternative lead and lead set types.

II. Antenna Diversity Using Multiple ECG-Lead Antennas

Another feature of the invention, referred to herein as ECG lead antennadiversity, involves providing two or more separate ECG-lead antennas,and switching between these antennas to provide spatial antennadiversity. This feature is implemented in the preferred embodiment usingECG leads with non-coaxial, unshielded lead wires 42 of the typeillustrated in FIG. 1. The ECG lead antenna diversity feature may alsobe implemented using ECG leads with other types of lead wires, such aswith coaxial or other shielded lead wires in which case the outershields may be used for the antennas. The two or more antennas arepreferably formed by effectively dividing the complete set of leads intotwo or more corresponding, mutually exclusive subsets of leads.

FIG. 2 shows, for a 5-lead set 32 of the type shown in FIG. 1, how theECG lead antenna diversity feature is implemented in the preferredembodiment. The drawing is also representative of implementations inwhich coaxial or other shielded ECG lead wires are used. Specifically,the illustrated antenna conductors 44 can be the shields of coaxial orother shielded lead wires; these shields may extend along the entirelength of each lead wire, or along only a portion of each lead wire. TheECG conductors 46 are omitted from FIG. 2 to simplify the drawing.

In this embodiment, the antenna conductors 44 of the Chest and Right Legleads 38 are electrically connected to form a first antenna, ANT1; andthe antenna conductors of the Left Arm, Left Leg and Right Arm leads areelectrically connected to form a second antenna, ANT2. These connectionsare preferably made inside the connector plug 34, as shown, so that onlytwo antenna connections are needed between the connector plug 34 and theconnector 36. The general configurations and positions of the antennasduring patient monitoring are depicted in FIG. 3. As discussed below,although the connections between antenna conductors 44 are fixed in thisembodiment, switched connections may alternatively be used so that theantennas may be formed or defined dynamically.

As further depicted in FIG. 2, each antenna line ANT1, ANT2 is connectedto an RF antenna switch 50 via a respective impedance matching circuit52A, 52B. In one implementation, the impedance matching circuits 52A,52B match the approximately 600 ohm impedance of the ECG-lead antennasANT1, ANT2 with the approximately 50 ohm impedance of the printedcircuit boards used within the ambulatory transceiver 30. The impedancematching circuits may be omitted in embodiments that use coaxial leads;In addition, as discussed below, dynamically controlled impedancematching circuits may be used to compensate for changes in antennaimpedances.

The antenna switch 50 selects between the two antennas, ANT1 and ANT2,and connects the selected antenna to an RF transceiver circuit 56 (“RFtransceiver”). The RF transceiver 56 uses the currently selected antennaboth to receive and transmit RF data packets. The RF transceiver 56includes or is connected to a decision and control logic circuit 58 thatcontrols the switch 50 via a selection signal, ANT—SEL. This circuit 58preferably selects between the antennas based on information aboutreceived signal transmissions. This information may, for example,include one or more of the following: signal strength measurements, dataindicating whether transmissions are being received error-free, andimpedance measurements of antennas or antenna elements. The circuit 58may also select between the antennas based on the quality of the signalreceived from the transceiver 30 by a base station, as reported back tothe transceiver by the base station.

As will be apparent to those skilled in the art, a number of variationsto the design shown in FIG. 2 are possible. For example, each antennacould be formed from a different set of antenna conductors 44 than thoseshown (e.g., the RL lead can be used for the first antenna, and the LA,C, LL and RA leads can be used for the second antenna). In addition, theECG leads 38 could be grouped or divided to provide three, four, or fiveseparate antennas, rather than two. Further, rather than using “fixed”antennas as shown, the antenna conductors 44 could be connected to aswitch (as in FIG. 8, discussed below) that dynamically selects the ECGlead or leads 38 to use as the antenna. In addition, each of the two ormore antennas could be connected to its own, respective RF receivercircuit to allow the antennas to receive data transmissionsconcurrently, so that a packet will be successfully received if any ofthe antenna-receiver pairs successfully receives the packet. Further,the A/B type switch 50 may be replaced with a switch capable ofconnecting the two fixed antennas to form a third antenna option,ANT3=ANT1+ANT2.

Further, one or more additional antenna conductors may be providedoutside the leads themselves for use as additional antenna elements. Forexample, an antenna wire may be bonded to or dangled from the plastichousing of the transceiver 30, and may be incorporated into one or moreof the ECG lead antennas as an additional element.

Any of a variety of antenna selection methods may be used in the systemof FIG. 2. For example, in one embodiment, whenever the RF transceiver56 fails to successfully receive a packet expected from an access point(e.g., detects a CRC error), the circuit 58 automatically switches tothe other antenna; this antenna is thereafter used until another packetis missed. In another embodiment, at the beginning of each base stationtransmission (which occurs during a predefined timeslot of a TDMA framein the preferred embodiment), the ambulatory transceiver 30 samples thesignal strength of the received signal on one antenna (ANT1 or ANT2) andthen the other. The antenna having the higher signal strength is thenselected for use—both to receive the packet transmitted by the basestation and to transmit the next packet—unless a packet was missed withthat antenna on the immediately preceding TDMA frame.

In addition, in embodiments in which frequency hopping is used, theambulatory transceiver 30 may perform a separate antenna selectionanalysis for each frequency of the hopping sequence. The antennaselections would thus reflect frequency dependencies that may exist. Asdiscussed below with reference to FIGS. 7 and 8, the antenna mayalternatively be selected in-whole or in-part based on antenna impedancemeasurements. In addition, the antenna could be selected based in-wholeor in-part on feedback from an access point or other base station withwhich the ambulatory transceiver 30 communicates. Further, inembodiments in which each base station has two antennas, A and B, aprotocol may be used in which the ambulatory transceiver 30 samples thesignal strength for each of the four possible antenna combinations (A:1,A:2, B:1 and B:2), and selects the antenna combination that produces thebest result.

Rather than selecting between the available antennas based onmeasurements, the transceiver may be designed to simply transmit eachpacket of physiologic data on each antenna to provide redundancy. Forexample, if two antennas are provided, the transceiver could transmiteach packet using antenna A and then antenna B to provide a combinationof time and space diversity. In one such embodiment, each access pointor other base station has two antennas/diversities, such that eachtransmission can take four possible paths. Yet another approach is touse one antenna as the transmit antenna, and another antenna as thereceive antenna.

In embodiments in which the telemetry unit is a unidirectionaltransmitter, the transmitter may select between the multiple ECG-leadantennas based solely on antenna impedance measurements. Alternatively,the transmitter could simply transmit the patient's data separatelyusing each ECG lead antenna, as described above.

Antenna diversity as set forth above may also be implemented using leadsand lead sets for sensing other types of physiologic data, including EEGlead sets, leads with oscillometric blood pressure sensors, and leadswith SpO₂ sensors. For instance, in a 2-lead set in which one of theleads senses SpO₂ levels and the other lead senses blood pressure, twosingle-lead antennas may be provided, each of which is formed from aconductor within a respective lead. The telemetry unit may use anyappropriate antenna switching method, including those described above,to switch between these two antennas.

III. ECG Connector Plug and Example Antenna Connections

FIG. 4A illustrates the configuration of the connector plug 34 infurther detail. The plug includes eight contacts, labeled P1-P8, forconnecting with eight corresponding contacts (not shown) on theconnector 35. In one embodiment, the plug 34 is a custom bulkheadconnector mating connector with a Bayer Makroblend EL700 connectorshell, socket contacts, and a Santoprene overmold that meets EN 529-1989IPX7 requirements. FIG. 4B, which is a cross sectional view taken alongline 4B—4B in FIG. 4A, further illustrates the connector plug 34 and thelead wires 42 for the 5-lead embodiment of FIGS. 1-3.

In the preferred embodiment of the transceiver system, the sameconnector plug design is also used within other ECG lead setconfigurations. FIGS. 5A-5G illustrate the electrical connections withinthe connector plug 34 for each of the seven ECG lead set configurations.All of these lead sets provide two, fixed antennas, and may be used withthe same ambulatory transceiver device 30 (e.g., a device with theantenna selection circuit depicted in FIGS. 2 and 6). FIG. 5Aillustrates the interconnections used to implement the antenna designshown in FIG. 2. In this embodiment, the antenna conductors 44 of the RLand C leads are connected to P1, and the antenna conductors of the LA,LL and RA leads are connected to P8. The remaining contacts (except forP19, which is unused) carry the patient's ECG signals. The antennaconductors 44 are preferably connected in this and the other illustratedlead set configurations of FIG. 5 by inserting the ends of thecorresponding antenna conductors 44 into a common socket contact of theplug 34.

FIG. 5B illustrates a 5-lead set in which the antenna conductor 44 ofthe RL lead forms the first antenna, and the antenna conductors 44 ofthe LA, C, LL and RA leads are all connected to form the second antenna.FIG. 5C illustrates a 3-lead set in which the antenna conductor 44 ofthe LA lead forms the first antenna, and the antenna conductors 44 ofthe LL and RA leads are connected to form the second antenna. FIG. 5Dillustrates a 4-lead set in which the antenna conductors 44 of the RLand LA leads are connected to form the first antenna, and the antennaconductors 44 of the LL and RA leads are connected to form the secondantenna.

FIG. 5E illustrates a 4-lead set in which the antenna conductor 44 ofthe RL lead forms the first antenna, and the antenna conductors 44 ofthe LA, LL and RA leads are connected to form the second antenna. FIG.5F illustrates a 6-lead set in which the antenna conductors 44 of the RLLA and C1 (Chest 1) leads are connected to form the first antenna, andthe antenna conductors 44 of the LL, RA, and C2 (Chest 2) leads areconnected to form the second antenna. FIG. 5G illustrates a 6-lead setin which the antenna conductor 44 of the RL lead forms the firstantenna, and the antenna conductors 44 of the LA, C1, LL, RA and C2leads are connected to form the second antenna. Various otherconfigurations are possible, including configurations that provide threeor more antennas.

The lead set designs shown in FIGS. 5A-5G preferably use non-coaxialleads 38 of the type shown in FIGS. 1A and 1B. As will be recognized,however, these designs can also be implemented using coaxial lead wires.The use of coaxial lead wires to implement these and othermultiple-antenna ECG lead sets is considered part of the presentinvention.

IV. Transceiver Architecture and Defibrillation Pulse ProtectionCircuitry

FIG. 6 illustrates the circuitry of a preferred embodiment of theambulatory transceiver device 30 in further detail. As mentioned above,this circuit may be used with each of the seven ECG lead sets shown inFIGS. 5A-5G . The circuit may also be used with other lead sets thatprovide two fixed antennas. In this embodiment, the RF antenna switch 50is connected to a removable RF module 64. The RF module includes amicrocontroller 66, such as an Atmel ATmega 103L with built-in RAM andROM, and a radio circuit 68. The microcontroller 66 and radio circuit 68collectively implement the RF transceiver 56 depicted in FIG. 2. Asshown in FIG. 6, this microcontroller 66 also generates the controlsignal ANT—SEL used to select between the two antennas. The task ofselecting between the antennas may alternatively be implemented withindedicated hardware, such as an ASIC (application-specific integratedcircuit), a separate microprocessor device, or by a combination ofdevices.

As further depicted in FIG. 6, each ECG conductor 46 (FIG. 1B) of thelead set connects to a respective ECG signal line (LA, RA and RL signallines shown) within the ambulatory transceiver 30. The RL signal line isconnected to ground, as is conventional. The remaining five ECG signallines (LA, C1, C2, RA, and LL) are connected to an analog signalconditioning circuit 72 via respective current-limiting resistors 70. Asdiscussed below, these current-limiting resistors 70 are preferablysurface mount components. Each current-limiting resistor 70 ispreferably a single component, but may alternatively be in the form oftwo or more resistor components connected in series.

Each current-limiting resistor 70 has a “hot” side (designated by thesubscript “H”) which connects to an ECG conductor 46 of the lead set,and a “cold” side (designated by the subscript “C”) connected to thesignal conditioning circuit 72. The cold side of each resistor 70 isadditionally connected to ground via a respective bi-directionalTransient Voltage Suppression (TVS) circuit 76. Each resistor 70 andcorresponding TVS circuit 76 form a protection circuit that protects thecircuitry of the ambulatory transceiver 30 from potential damage in theevent that a defibrillation pulse is applied to the patient.Specifically, when a defibrillation pulse is applied, each TVS circuit76 opens (becomes conductive), as necessary, fast enough to prevent thevoltage on the hot side of the corresponding resistor 70 from exceedingabout 1000 volts. The likelihood of damage to the signal processing orother circuitry or the transceiver caused by arcing is thereby reduced.Each resistor 70 provides an additional level of protection by limitingcurrent flow during application of the defibrillation pulse.

In addition to protecting the circuitry of the transceiver 30, theprotection circuit protects clinicians that may be in contact with thetransceiver from conducting some of the pulse. The protection circuitalso reduces the likelihood that some of the defibrillator energy willbe “stolen” (reducing the effectiveness of the procedure) as a result ofa low resistance path across the ECG lead set.

An important aspect of the protection circuit design involves the use ofTVS circuits 76 having a very low junction capacitance—preferably lessthan 10 pF (picofarads) each, and more preferably less than 5 pF each.Each TVS circuit 76 also preferably has a breakdown voltage of less than10 volts and an activation time of less than 20 microseconds. In oneembodiment, one or more surface mounted USB0812C integrated circuits(TVS arrays) available from Microsemi Corporation are used to providethe TVS circuits 76. The data sheet for the USB0812C device is herebyincorporated herein by reference. The use of such low capacitance,bidirectional TVS. circuits 76 advantageously allows the relativelylarge, high-power (e.g., one Watt), non-surface-mount resistorsconventionally used for defibrillation pulse protection to be replacedwith the smaller resistors 70, which may advantageously be surfacemounted resistors. The size and manufacturing cost of the of thedefibrillation protection circuitry can thereby be reduced. Eachresistor 70 preferably has a power rating of less than 0.5 Watts. In oneembodiment, 90 k ohm, 0.1 Watt surface-mount resistors 70 are used, andare mounted to a printed circuit board (not shown) of the bulkheadconnector.

The protection circuit design also provides improved safety in thepresence of faults. For example, if either a resistor or a TVS circuitfails, there is still some protection. In contrast, in prior art devicesthat use a pure resistor protection circuit, if one of thecurrent-limiting resistors fails to a short then there is no protection.This protection circuit design may also be incorporated into other typesof electronic devices that receive signals from an ECG lead set,including but not limited to bedside monitors, Holter recorders,diagnostic ECG machines, and portable defibrillators.

As further illustrated in FIG. 6, the analog ECG signal outputs of thesignal conditioning circuit 72 are converted to corresponding digitalsignals by an analog-to-digital (A/D) converter 80. These digital ECGsignals are processed by a second microcontroller 82, such as aMitsubishi M16C/62 device with built-in RAM and ROM, before being passedto the RF module 64 for transmission. This microcontroller 82 is alsoresponsible for the following tasks: (1) controlling the signalconditioning circuit 72; (2) controlling and providing an interface fortwo serial ports (labeled 1 and 2), which are accessible via the12-contact data I/O connector 86; (3) driving LEDs on the housing of theambulatory transceiver 30; (4) detecting and processing buttondepression events; and (5) detecting fault conditions in the leadsetconnection (e.g. a poor electrode to skin contact or a failure in thelead conductor).

One of the two serial ports (labeled port 1) is used primarily to uploadcode updates. The second serial port (labeled port 2) is used to connectthe ambulatory transceiver 30 to an external device (typically anAC-powered medical device) having a standard port, such as a port whichoperates according to one or more of the following interface standards,the specifications of which are hereby incorporated herein by reference:RS-232, RS-422, RS-485, EIA-562, TTL. The ambulatory transceiver 30transmits the physiologic or other data received from the externaldevice together with the patient's ECG waveforms (preferably within thesame packets), allowing such data to be remotely monitored in real time.

V. Opto-Isolation Circuit

As illustrated in FIG. 6, port 2 preferably includes an opto-isolationcircuit 88 which isolates the port in accordance with regulationUL-2601. While the external device is connected, the opto-isolationcircuit 88 electrically isolates the external device from the ECG leadset, and thus protects the patient from potential shock caused by theexternal medical device. The opto-isolation circuit thereby allows thetransceiver 30 to communicate with the external device and receive ECGsignals from the lead set simultaneously.

In accordance with one aspect of the invention, the hot side of theopto-isolation circuit is powered by the external device by stealingpower from the RS-232 or other standard port. Conventional powerstealing methods may be used for this purpose. An important benefit ofusing power stealing to power the hot side of the opto-isolation circuitis that it eliminates the need for a separate, isolated power supply.

In one embodiment, the opto-isolation circuit 88 implements aquasi-RS-232 interface that supports a wide range of existing medicaldevices having RS-232 ports. The opto-isolation circuit 88 mayalternatively be entirely RS-232 compliant. In addition, the circuit 88may be designed to support multiple different interface standards.

In one embodiment, the opto-isolation circuit 88 with power stealing isalternatively incorporated into the cable 37 (FIG. 1) that connects thetransceiver 30 to the external device. In this embodiment, separatecables are provided for some or all of the different interface standards(e.g., RS-232, RS-422, RS-485, EIA-562, and TTL), each with a different,interface-specific version of the opto-isolation circuit 88. Theappropriate cable can then be selected to match the interface of theexternal device.

In other embodiments, an opto-electric circuit 88 as described above maybe incorporated into or used with other types of patient-attached,battery-powered devices that receive a patient's ECG signals. Forexample, the circuit 88 can be incorporated into a unidirectionaltransmitter, a Holter recorder, a mobile ventilator, or a PDA; or may beincorporated into a cable that connects such a device to the externaldevice.

VI. Dynamic Impedance Matching

FIG. 7 illustrates another inventive feature that may be incorporatedinto the transceiver design, or into a unidirectional transmitter thatuses lead conductors as antenna elements. In this embodiment 30′, theimpedance matching circuits 152 are dynamically controlled based on realtime impedance measurements of the antennas, ANT1 and ANT2.Specifically, an impedance detector 150 monitors the respectiveimpedance of each antenna (e.g., by monitoring signal reflections causedby impedance mismatches), and outputs control signals that reflect thesemeasurements. The control signals are used to dynamically adjust theimpedance matching circuits 152, as necessary, to generally maintainproper tuning between the antennas and the transceiver circuitry. Wellknown impedance matching techniques used in other types of RFapplications may be used for this purpose.

In the embodiment shown, the control circuitry for controlling thedynamic impedance matching circuits 152 is included within the impedancedetector 150 block. The actual control path for controlling theimpedance matching circuits 152 may include a programmed processor, suchas one of the microcontrollers 66, 82 shown in FIG. 6. The controller orcontrol circuit may adaptively correct for detected impedance imbalancesusing a conventional feedback process.

The use of dynamic impedance matching provides additional protectionagainst the effects of bed rails and other sources of antenna detuning.For example, if the impedance of ANT1 drops as the result of a leadbeing positioned close to a bed rail, the corresponding impedancematching circuit 152 will automatically be adjusted to compensate forthe impedance drop. In many cases, this adjustment will be sufficient tomaintain the affected antenna in an operable state.

As depicted by the dashed arrow in FIG. 7, the impedance measurementsmay also be incorporated into the logic used to select between theantennas. For example, when the impedance of an antenna falls outside apre-selected range, that antenna may automatically be excluded from use.

The use of dynamic impedance matching as described above may also beused in designs that do not provide antenna diversity. For instance, allof the antenna conductors 44 could be connected to form a singleantenna; the impedance of this single antenna could then be monitored,and its matching circuit 152 adjusted, in the same manner as describedabove. Further, although dynamic impedance matching is preferableimplemented using leads with unshielded lead wires of the type describedabove, the feature may also be used with lead sets having coaxial orother shielded lead wires.

The dynamic impedance matching feature as set forth above may also beused with leads and lead sets for sensing other types of physiologicdata, including but not limited to EEG, SpO₂, and blood pressure data.

VII Dynamic Selection of Antenna Conductors

The ECG-lead antennas illustrated in the preceding drawings are “fixed”or “statically defined,” meaning that each antenna is formed using afixed set of one or more ECG leads. One possible enhancement to thedesign is to add a switch for dynamically selecting the antennaconductor(s) 44, and any additional antenna elements that may beprovided as described above, to use as the antenna. FIG. 8 illustratesone embodiment of this feature. Each antenna conductor 44 is connectedto a matrix switch 160 capable of selecting any one or more ECG leads touse as the antenna. For a five-lead set as shown, the switch is thuscapable of forming 31 different antennas corresponding to the 2⁵−1possible combinations of ECG leads. More generally, if the lead set hasN antenna conductors (one per lead), the switch can form 2^(N)−1possible combinations. The antenna conductor(s) selected for use as theantenna are connected by the switch 160 as a unit (single antenna) tothe RF transceiver 56. In the embodiment shown, the connector plug 134connects each antenna conductor 44 to a corresponding signal line withinthe transceiver. Alternatively, the switch 160 could be formed withinthe connector plug such that fewer connections are needed.

Any of a variety of antenna selection algorithms can be incorporatedinto the decision and control logic 58 to control the matrix switch 160.In one embodiment, for example, the ambulatory transceiver 30 operatesin either a “two-antenna diversity” mode or an “exception” mode, whichmay be implemented as follows:

Two-antenna diversity mode: While in this mode, the ambulatorytransceiver 30 selects between two “default” antennas, ANT1 and ANT2,each of which is formed from a different respective subset of ECG leads(e.g., ANT1=RL and C, and ANT2=LA and LL and RA). Any of the antennaselection methods described above may be used for this purpose. When Nconsecutive packets are missed, the transceiver switches to the“exception” mode.

Exception mode: Upon entering this mode, the ambulatory transceiver 30attempts to communicate with the base station using each possiblecombination of ECG leads 38 as the antenna, according to a predefinedsequence. For example, the transceiver may initially use each ECG leadindividually, then each possible pair of leads, and then each possiblecombination of three leads, and so on until all combinations have beenattempted. This sequence may be statically defined, or may be based onhistorical data recorded within the transceiver's memory about the leadcombinations that have previously produced a successful result. Once apacket is successfully received, the ambulatory transceiver 30 continuesto use the selected antenna, and attempts to revert back to the“two-antenna diversity” mode on every X^(th) attempt to receive apacket. The transceiver switches back to the two-antenna diversity modewhen either (1) a packet is successfully received during an attempt toreturn to the two-antenna diversity mode, or (2) M consecutive packetsare missed using the antenna selected in the exception mode.

As a variation of the above approach, the transceiver 30 could use theentire set of ECG leads as the default antenna (i.e., interconnect allof the antenna conductors), and switch to the “exception mode” when aproblem is detected with the default antenna (e.g., packets are missed,and/or signal strength falls below a threshold).

As illustrated in FIG. 8, the matrix switch 160 may optionally beintegrated with an impedance detector 150′ that monitors the impedanceof each antenna conductor 44 individually. These impedance measurementsmay be appropriately incorporated into the antenna selection process.For example, when the impedance of a particular lead's antenna conductor44 falls below a predefined threshold, the exception mode algorithm mayautomatically skip over all lead combinations containing that lead. Asfurther illustrated, the impedance measurements may additionally oralternatively be used to control a dynamic impedance matching circuit152 in the manner described above.

Although all of the antenna conductors 44 are passed through to theswitch in the embodiment in FIG. 8, a hybrid approach is also possiblein which only some of the antenna conductors 44 are passed through. Forexample, referring to FIG. 8, the RL and C conductors 44 could be passedthrough to the switch 160, and the LA, LL and RA conductors 44 could beconnected within the plug 134 (fixed connections) and passed to theswitch 160 as a single antenna, ANT. The switch 160 could then selectbetween the following seven possible antennas: RL alone, C alone, ANTalone, RL+C, RL+ANT, C+ANT, and RL+C+ANT.

Another variation is to use a matrix switch that has two separateoutputs, each of which is connected to a respective receiver. With thisconfiguration, the ambulatory transceiver 30 can receive transmissionsusing two antennas simultaneously, each of which may be formed from anycombination of one or more leads.

The matrix switch embodiment set forth above may also be used with leadsand lead sets for sensing other types of physiologic data, such as EEGsignals.

VIII. Phased Antenna Array

FIG. 9 illustrates another feature that may be incorporated into theambulatory transceiver design to improve performance. In thisembodiment, the antenna conductors 44 of at least some, and preferablyall, of the ECG leads 38 (and/or other types of leads such as thosedescribed above) are used as individual elements of a phased antennaarray. One or more additional antenna elements (not shown) may beprovided outside the lead set, as described above, to increase thenumber of elements within the array. As illustrated, each antennaconductor 44 (and each additional antenna element, if any) is coupled toa respective phase shifter 180. The antenna conductors 44 are alsoconnected to a phase detector and control circuit 182 (“controller”)which controls the phase shifters 180. The phase shifters 180 are alsoconnected via a common electrical node 186 to the RF transceiver 56.

In one embodiment, each phase shifter 180 can be placed into an “off”mode in which it passes no energy. This is logically equivalent tohaving a SPST switch in series with the phase shifter, though inpractice the two functions may be integrated into the same device. Thisfeature permits an antenna to be formed using less than all of theantenna elements, as may be desirable in some circumstances.

During receive events, the controller 182 measures the differencesbetween the phases of the respective signals received by the antennaconductors 44 (and any additional antenna elements) from the basestation. Based on these measurements, the controller 182 adaptivelyadjusts the phase shifters 180 as necessary to bring these signals intophase with one another. The controller may also place one or more phaseshifters 180 in its “off” mode. The phase-adjusted signals are summed atnode 186 to produce the RF signal processed by the transceiver 56.During transmission events to the same base station, the same phaseshifter settings are used to modify the phase of the transmission signalseparately for each antenna conductor 44. The beam is thus effectivelysteered back in the direction of the base station, improving thelikelihood of reception.

In embodiments in which the ambulatory transceiver 30 concurrentlymonitors transmissions from multiple devices (e.g., to evaluatecandidate access points with which to establish a connection), thecontroller 182 may maintain in its memory a history of recent phaseshifter settings used to communicate with each such device. Just priorto a transmission timeslot of such a device, the controller may thenretrieve the device's settings and initialize the phase shifters 180accordingly. In embodiments that use frequency hopping, the transceivermay also capture and store data regarding any frequency dependencies inthe phase shift settings. This frequency dependency data may be used toadjust or initialize the phase shifters 180 as the transceiver 56switches from one frequency to another.

The controller 182 may also support a “scan” mode in which the antennabeam is scanned in an attempt to establish connectivity with a basestation. This feature may be used, for example, to search for a basestation when no connection currently exists, or to evaluate basestations as “roam” or “switch-over” candidates when a connection exists.The process of scanning for a base station involves initially scanningthe antenna beam passively (i.e., without transmitting) in an attempt tolocate a “good” base station. Once the transceiver 30 locates a goodbase station, the transceiver may transmit to that base station arequest for a connection, as described generally in U.S. Pat. No.5,944,659.

Conventional circuits and methods for controlling phased antenna arraysmay be used to perform the foregoing functions. The lead wires 42 usedto provide the antenna elements of the phased array are preferably ofthe type shown in FIG. 1 (non-coaxial), but may alternatively becoaxial. The process of scanning the antenna beam may be controlled byfirmware executed by a microcontroller of the transceiver 30, or mayalternatively be controlled in-whole or in-part by application-specifichardware.

In one embodiment, the phased antenna array is implemented incombination with dynamic impedance matching as described above.Specifically, a dynamically-controlled impedance matching circuit 152(not shown in FIG. 9) is provided in-line with each antenna conductor 44on the ECG-lead sides of the phase shifters 180.

IX. Conclusion

Although the various inventive features have been disclosed in thecontext of certain preferred embodiments and examples, it will beunderstood by those skilled in the art that the present inventionextends beyond the specifically disclosed embodiments to otheralternative embodiments and/or uses of the invention and obviousmodifications and equivalents thereof. Thus, the present invention isdefined by the following claims.

What is claimed is:
 1. A lead set, comprising: a lead set connectorconfigured to connect the lead set to a device, the lead set connectorincluding a plurality of contacts for conveying electrocardiograph (ECG)signals to the device, the lead set connector further including at leastone antenna contact for connecting the device to an antenna of the ECGlead set; and a plurality of external ECG leads that extend from theconnector, at least one of the ECG leads comprising a flexible lead wireextending between the lead set connector and an ECG electrode connector,the lead wire comprising a first conductor coupled to the ECG electrodeconnector to receive an ECG signal of a patient, and a second conductorwhich extends alongside the first conductor in a non-coaxial arrangementand is insulated from the first conductor, the second conductor beingelectrically connected to the antenna contact of the lead set connectorwherein the second conductor is not used to transmit an ECG signal andis used as at least a portion of the antenna.
 2. The lead set as inclaim 1, wherein the second conductor extends substantially from thelead set connector to the ECG electrode connector.
 3. The lead set as inclaim 1, wherein the antenna contact of the lead set connector iselectrically connected to a conductor within at least one additional ECGlead, such that the antenna is formed from multiple ECG leads.
 4. Thelead set as in claim 1, wherein the lead set connector comprises asecond antenna contact for connecting the device to a second antenna ofthe lead set, whereby the lead set supports antenna diversity byproviding multiple antennas for use by the device.
 5. The lead set as inclaim 4, in combination with a telemetry device that connects to thelead set and uses the multiple antennas to provide antenna diversity. 6.The lead set as in claim 5, wherein the telemetry device is atransceiver device.
 7. The lead set as in claim 1, wherein the lead setconnector comprises at least one antenna contact for each of theplurality of ECG leads, each antenna contact connected to a respectiveantenna conductor of a respective ECG lead such that each ECG lead maybe used independently to provide an antenna.
 8. The lead set as in claim7, in combination with a transceiver device that connects to the leadset, the transceiver device comprising a switch capable ofinterconnecting two or more of the antenna conductors to dynamicallyform an antenna.
 9. The lead set as in claim 7, in combination with atransceiver device that connects to the lead set and uses the antennaconductors as individual elements of a phased antenna array.
 10. Thelead set as in claim 7, in combination with a transceiver device thatconnects to the lead set, the transceiver device comprising an impedancedetection circuit that monitors impedance values of the antennaconductors.
 11. A telemetry device, comprising: a portable radiofrequency (RF) transmitting unit adapted to be worn by a patient; and alead that extends from the RF transmitting unit and attaches externallyto the patient, the lead comprising a flexible lead wire comprising afirst conductor and a second conductor that extend side by side in anon-coaxial arrangement; wherein the first conductor carries aphysiologic data signal from the patient to the RF transmitting unit,and the RF transmitting unit uses the second conductor as at least aportion of a telemetry antenna for transmitting the physiologic datasignal, the second conductor not carrying a physiologic data signal fromthe patient.
 12. The telemetry device of claim 11, wherein the secondconductor extends substantially an entire length of the lead wire. 13.The telemetry device of claim 11, wherein the lead comprises an ECGelectrode.
 14. The telemetry device of claim 11, wherein the leadcomprises an electroencephalogram (EEG) electrode.
 15. The telemetrydevice of claim 11, wherein the lead attaches to the RF transmittingunit by a lead set connector plug.
 16. The telemetry device of claim 11,wherein the lead is fixedly attached to the RF transmitting unit. 17.The telemetry device of claim 11, wherein the RF transmitting unit is atransceiver unit.
 18. The telemetry device of claim 11, wherein the RFtransmitting unit is a unidirectional transmitter unit.
 19. Thetelemetry device of claim 11, wherein the lead is part of a lead set theprovides multiple antennas, and the RF transmitting unit automaticallyswitches between the multiple antennas to provide diversity.
 20. Thetelemetry device of claim 11, wherein the lead is part of a lead set theprovides multiple antenna elements, and the RF transmitting unit usesthe multiple antenna elements to provide a phased antenna array.
 21. Thetelemetry device of claim 11, wherein the RF transmitting unit monitorsand dynamically compensates for changes in an impedance of the telemetryantenna.